Cultivated cucumber (Cucumis sativus var. sativus L.) is an important vegetable crop worldwide. It belongs to the family Cucurbitaceae. It is thought to originate from South East Asia from wild ancestors with small, bitter fruits, such as Cucumis sativus var. hardwickii. 
The cultivated cucumber genome has seven pairs of chromosomes (n=7) and a haploid genome size of about 367 Mb (Megabases) with an estimated total of about 26,682 genes. The cucumber genome was the first vegetable genome to be sequenced (Huang et al. 2009, Nature Genetics, Volume 41, Number 12, p 1275-1283 and http://www.icugi.org/cgi-bin/gb2/gbrowse/cucumber_v2/).
Yield of cultivated cucumber has not increased much over the last decades. Shetty and Wehner 2002 (CropSci. 42: 2174-2183) screened the USDA cucumber germplasm collection for fruit quality and fruit yield under field conditions in North Carolina (USA) and suggest that high yielding cultigens identified in their study can be used to develop high yielding cultivars.
WO2009/082222 used on of the accessions identified by Shetty and Wehner in 2002 (supra), the Turkish Beit-Alpha landrace PI 169383 to identify QTLs for fruit weight of harvest stage cucumbers on linkage group 3 and/or 4 of PI 69383 and seeds were deposited of this accession under accession number NCIMB41532. This donor is a Turkish Beit Alpha landrace of cucumber (which is not a wild relative of cucumber) and does not contain the SNP markers of the instant invention. Further, the patent application describes cucumber plants comprising a whole chromosome 3 substitution, i.e. the whole chromosome 3 is from the donor PI169383.
Wei et al. 2014 (BMC Genomics 15: 1158, p 1-10) disclose mapping of immature and mature fruit length and immature fruit weight in a population derived from a cross between a Chinese cucumber inbred line (CC3) and NC76. NC76 was developed from a landrace of Cucumis sativus var. sativus from Afghanistan (P1246930) (which is not a wild relative of cucumber) and has short fruits (7˜10 cm). By crossing the short fruited NC76 with the long fruited CC3, they mapped QTLs in a segregating F2 population for (immature and mature) fruit length and immature fruit weight, as presented in additional file 6. They found two QTLs for immature fruit length (fl3.1 and fl3.2), two QTLs for immature fruit weight (fw3.1 and fw3.2) and one QTL for mature fruit length (mfl3.1) on Linkage Group 3 (LG3), in addition to another QTL for immature fruit length on LG 1 (fl1.1) and LG6 (fl6.1), but they do not disclose any information on total fruit yield.
Fazio et al. 2003 (Theor Appl Genet 107: 864-874) genetically mapped a number of traits, including cumulative fruits per plants over three harvests and morphological traits such as little leaf (11′). Their linkage group 6 appears to correspond to the physical chromosome 3. They mapped one QTL called fp16.1 which had a positive effect on cumulative fruit number per plant over three harvests (fruit number per plant was measured at three harvest points) to marker OP-AG1-2 at position 40.8 cM. It was only detected at one location. They also mapped another QTL called nfp6.2 which had a positive effect on number of fruits per plant to marker AK5-SCAR at position 38.6 cM. This QTL was detected at one location and was detected in all three harvests at that location. These QTLs are physically located on the lower half of chromosome 3 (around 3.0 Mb), while the QTL of the present invention is located on the upper half of chromosome 3, between 21.50 Mb and 27.23 Mb of chromosome 3.
Still, there remains a need for identifying QTLs for fruit yield in cucumber to be able to increase fruit yield of modern cucumber varieties.